I've been looking at the Ultra 120-extreme for a new rig I'm gonna be building soon, and I'm just wandering if there's a better cooler for under $100. I've heard nothing but good about the 120 extreme, so I'm not sure if I want something else or not.

I'm going to be putting this on an E4600 in an EVGA 680i T1 version, and I want the max possible overclock without hitting 60 degrees as I need this rig to last me for a while.

Also, how is the NB cooler on this board? Is it good, or should I try to find a better one?

You will likely reconsider the MB you seek!
The Gigabyte GA-P35-DS3R is a good inexpensive alternative, or an even better OCer is the DS3L... those for the "Budget System:
You should post your budget and get some opinions in the Intel/MB section

The U120 E will likely need a serious lapping though, mine was very warped! I had to file it down first, then lap it it had a bow like this... ( right in the middle of it. Don't get me wrong, its a great HS, just needs a little attention